Fermentation of sugars and starches derived from corn and other farm products has been widely used to produce ethanol, and today in the United States, ethanol is the largest biofuel used in the transportation fuels markets. There are many technologies that produce biofuels from biomass. For example, ethanol may be produced from lignocellulosic biomass. Isobutanol, as another example, can be formed from the fermentation of sugars which can be formed via the breakdown of cellulose. For example, solutions of up to approximately 2% by weight isobutanol in microbial growth have been produced in certain fermentation processes (Frances Arnold, “The Race for New Biofuels,” Engineering & Science, No. 2, 2008). U.S. Patent Application Publication No. 20070092957 describes fermentatively producing isobutanol using recombinant microorganisms.
Nevertheless, there has been much research in alcohol fermentation technologies aimed at producing higher alcohols, such as C4 and C6 alcohols, which are more compatible with petroleum gasoline than ethanol, especially with regard to reduced water solubilities, decreased phase separations, and enhanced volumetric heating values. Technologies are also being developed for the production of mixed alcohols, such as C2 to C7 alcohols.
As microbes are further developed to withstand higher concentrations of alcohol, it can be envisioned that isobutanol may compete with ethanol as a potential fuel component or chemical feedstock derived from renewable resources. Unfortunately, there exist concerns regarding direct blending of isobutanol and other higher alcohols into the gasoline pool due to odor and automotive component compatibility issues. For this reason, there is interest in conversion of light alcohols into feedstocks for conversion into fuels, petrochemicals, or other valuable end products.
U.S. Patent Application Publication Nos. 20090099401, 20090030239, 2008013274, 20080045754, 20080015395, 20080234523, and others, each filed by E.I. Dupont de Nemours and Company, Wilmington, Del., are directed to the conversion of bio-derived isobutanol to butenes and isooctenes, among other end products. Each of these processes react isobutanol over a homogeneous or heterogeneous acid catalyst to form the desired reaction product, either a butene or an isooctene (diisobutylene).
Unlike tertiary butanol, which can be readily converted via dehydration into its constituent isobutylene and then into fuel blend components, such as diisobutylene, as disclosed in U.S. Pat. No. 6,936,742, the conversion of other light alcohols often requires higher activity catalysts and more severe process conditions. Significant recycle rates may also be required to result in acceptable conversion levels. Additionally, with bio-derived alcohols, water may be present with the feed, and separation is often difficult due to the components having closer relative volatilities and potential for forming various azeotropes.
U.S. Patent Application Publication No. 20050112739 discloses several process schemes for the conversion of C3-C5 alcohols from biomass fermentation to form fuel components. In a typical process, the C3-C5 alcohols separated from a fermentation broth are first dehydrated to C3-C5 olefins, which are then hydroformylated with biomass-derived synthesis gas to produce C4-C6 aldehydes. The C4-C6 aldehydes are then condensed over base catalysts into unsaturated C8-C12 iso-aldehydes that are then hydrogenated to saturated C8-C12 iso-alcohols. The thus obtained iso-alcohols are then dehydrated to their corresponding iso-olefins which are subsequently hydrogenated to a mixture of C8-C12 paraffins.
U.S. Pat. No. 8,232,440 also discloses several process schemes for conversion of alcohols to fuel components. Biomass is converted to a carboxylic acid, which is then reacted with an olefin to produce an ester. The ester is then hydrogenolyzed to produce alcohol, which may be converted via an oligomerization process, for example, to produce hydrocarbon. Other patents related to use of or conversion of alcohols to fuels may include U.S. Pat. Nos. 7,737,315, 7,501,548, 7,414,164, and 7,559,961.